1. Field of the Invention
The present invention relates to a full bridge DC-DC converter, and particularly, to a full bridge DC-DC converter to which a current doubler is applicable.
2. Description of Related Art
In general, a full bridge direct current-direct current (DC-DC) converter converts a high DC voltage supplied from a high-voltage battery of a vehicle into a low DC voltage and provides an electric load of a vehicle such as an auxiliary battery with the low DC voltage.
In one of the conventional full bridge DC-DC converters, a full bridge DC-DC converter to which a current doubler is applicable is utilized. The full bridge DC-DC converter converts DC input voltage into alternating current (AC) voltage via a primary full bridge circuit (e.g., this full bridge circuit consists of FET (field effect transistor)), converts high AC voltage into low AC voltage via a transformer and outputs low AC voltage to an electric load via a secondary circuit of the transformer, which includes a secondary inductor and a diode. In the full bridge DC-DC converter to which a current doubler is applicable, the transformer is indispensable for reducing high voltage and isolating it from high voltage. When DC current is generated in the transformer, the transformer can be saturated.
In addition, causes exerting an influence on the saturation of the transformer may be mainly divided into causes of the primary side and causes of the secondary side of the transformer. The causes of the primary side may be due to FET Rds-on of the full bridge circuit, and the causes of the secondary side may be due to parasitic resistance of the inductor, a deviation of contact resistance between the inductor and the transformer and a deviation of contact resistance between the output diode and the transformer. A value of FET Rds-on, a value of parasitic resistance of the inductor, and a deviation value of contact resistance between the output diode and the transformer, which influences a saturation of the transformer, can be managed to reduce the effect on a saturation of the transformer.
However, since a coupling area between the inductor and the transformer is substantially small and the inductor is coupled to the transformer by a screw, even when a substantially small torque deviation is generated when the inductor is coupled to the transformer, a deviation of contact resistance between the inductor and the transformer has an effect on a saturation of the transformer.
In the conventional full bridge DC-DC converter as described above, the diode is firstly coupled to the secondary side of the transformer by the screw, thus generating a contact resistance when the inductor is coupled to the transformer by the screw and causing a current unbalance. In addition, DC offset current is generated at the primary side of the transformer due to the current unbalance thus causing a saturation of the transformer to be generated. When the transformer is saturated, current may rapidly increase to generate high current in a switch element. Therefore, a heat and loss of the switch element may increase and noise generation may increase.